1. The Field of the Invention.
The present invention is directed to a device useful for spinning fibers, especially those having a core component surrounded at least partially by at least one outer or sheath component, and to methods for using the device in the production of such fibers.
2. The Background of the Art.
Whereas natural fibers and many synthetic fibers are composed of a single material constituent, the further development of different types of polymers for synthetic fibers has allowed for the production of "multicomponent" fibers (such as "bicomponent" fibers); that is, a fiber having two or more distinct polymeric components. A unitary fiber can be spun from a blend of distinct polymeric components. More conventionally, the distinct polymeric components of a multicomponent fiber are provided separately in a particular geometric arrangement in the fiber; that is, a cross-section of the fiber evidences at least two distinct polymeric compositions in selected areas of the cross-section. The ability to use different materials in a single fiber allows the designer to alter or augment the properties from those of a single component fiber.
The particular geometric arrangement of multicomponent fibers can be categorized in a number of ways. True multicomponent fibers consist of two or more components divided, along the length of the fiber, into two or more essentially distinct regions, best observed in a cross-sectional view of the fiber. Typical cross-sectional geometries for bicomponent fibers include a side-by-side arrangement, such as two equal semi-circles in abutment, and sheath/core arrangement, which would appear as an annulus. Other types of multicomponent fibers have compositions which vary laterally along the fiber length, and which might appear in cross-section as a circle cut into four, six, or eight pie-like pieces. These are typically called "conjugate" fibers, and can be spun by such devices as described in JP 73-029,804, U.S. Pat. No. 2,758,553, and U.S. Pat. No. 3,230,972, in which an apparatus is provided in the device to divide the molten polymer stream into multiple feeds that converge into each individual spinneret orifice. Yet other fiber designs include a sheath or matrix having a plurality of cores. A general overview of multicomponent fibers is provided in "Bicomponent Fibers, a review of the literature," Report No. 44, published by TRI/Princeton, Princeton, N.J. (December 1993).
The spinning of concentric sheath/core fibers is typically achieved by separately channelling at least two spinnable liquids to a specially designed spinneret orifice from which the fiber is spun. The orifices are typically composed of inner and outer orifices, each supplying one of the spinnable components. Eccentric sheath/core fibers can be made by offsetting the inner orifice position with respect to the outer orifice geometry; sheath/core fibers can be provided such that one or both components are in a non-circular geometry by varying the geometry of the particular orifice through which the material is spun (such as described in GB 1,120,241). In various devices for spinning sheath/core fibers, the sheath component is metered between plates through which tubes or pipes run with the core component metered therethrough. The sheath component flows between the tube and the plate though which the tube runs and is co-spun with the core component. An example of such a device is described in JP 54-125717.
A "spinning pack" used for spinning multicomponent fibers generally contains an assembly including a number of elements for channeling the flows of each of the fiber components, optionally including one or more filters for each component, and a spinneret assembly including a plurality of orifices in which the flows are joined and then extruded as the spun fiber. Modification of the geometric arrangement of the fiber components and/or the relative ratios of the fiber components requires some retooling of the assembly, or the need to have a number of different spinneret assemblies which can be substituted for that being used to spin a particular multicomponent fiber.